Previous attempts to measure hypoxia have been biased because the techniques have been invasive, not repeatable or difficult to apply on a routine basis. There is great interest in trying to measure hypoxia in tumours as this could lead to individualized hypoxia-modifying therapy and prediction of treatment response. Additionally the investigators' knowledge of change in hypoxia over time is limited, but of great interest as individualised treatment, such as intensity-modulated radiation therapy (IMRT) is emerging.